Field of Art
The present disclosure relates to an ophthalmic apparatus, a system and a method for controlling an ophthalmic apparatus.
Description of the Related Art
An ophthalmoscope is an apparatus for gathering information about the interior portion of an eye (fundus). A simple direct view ophthalmoscope is a handheld device used by an optician to directly view the fundus which may include light source, aperture, and one or more lenses. An electronic ophthalmoscope use one or more sensors to obtain fundus images. These fundus images are then displayed to the optician with a display device. A high resolution ophthalmoscope may use lasers to obtain high resolution fundus images. A high resolution ophthalmoscope may also include adaptive optics to obtain even higher resolution fundus images. The adaptive optics can be used to compensate for the static and dynamic distortions introduced by the eye being examined. Examples of ophthalmoscopes include but are not limited to: ophthalmic image pickup apparatuses; fundus imaging systems; scanning laser ophthalmoscopes (SLO); adaptive optics scanning laser ophthalmoscope (AO-SLO); optical coherence tomographs (OCT); that utilize the interference of low coherence light; and adaptive optics optical coherence tomographs (AO-SLO). These ophthalmoscopes are important tools for the study of the human fundus in both normal and diseased eyes.
In AO-SLO and AO-OCT the adaptive optics (AO) are an optical correction system that measures the aberration of the eye and corrects for the measured aberration. The AO-SLO and AO-OCT may measure the wavefront of the eye using a Shack-Hartmann wavefront sensor system. A deformable mirror or a spatial-phase modulator is then driven to correct for the measured wavefront, and an image of the fundus is acquired, thus allowing AO-SLO and AO-OCT to acquire high-resolution images.
One of the challenges for gathering information about the fundus is that the reflectance at the retina (a part of the fundus) is very small (around 0.1%). Also, the amount of light that can be used to measure the fundus is limited by eye safety concerns. Thus, it can be difficult for a SLO to detect reflective light. One goal of an ophthalmoscope is to effectively light up the fundus so that the ophthalmoscope can gather a lot of reflective light. Providing enough illumination, by effectively lighting up the fundus, is the key to detecting enough light from the fundus whether it is reflective light and/or fluorescence light. If the illumination light enters the pupil off-center then a part of the illumination is kicked backed by the pupil and illumination light actually entering the eye is decreased. A result of this kick back is that reflective light from the fundus and light detected by the SLO decreases. Thus, in the prior art it was generally desirable that the SLO apparatus is set so that illumination light went through the center of pupil.
The inventors have determined that in some cases, where the prior art method of co-centering the center of the illumination beam with the center of the subject's pupil actually makes it harder to get a good fundus image. For example if the surface or interface being imaged has a tilt that is large then the reflected light may be directed away from the center of the pupil and the pupil will block some or all of the reflected light.